There is an article on Foxnews health about five foods that supposedly promote sleep. My immediate reaction to such a title is skepticism, as such "treatments" for insomnia rarely provide any lasting relief.
The first food is cottage cheese. The author says it helps sleep because it is a source of tryptophan, the same sleep-inducing amino acid in turkey. Unfortunately, consuming tryptophan is not likely to help most people who are struggling to sleep.
The next food mentioned is oatmeal. The author states that oatmeal is a slow-digesting carbohydrate that promotes serotonin release, the "feel good" neurotransmitter. He then says that serotonin is the sleep hormone - factually inaccurate on two counts - serotonin is not a hormone, it's a neurotransmitter, and many other neurotransmitters are thought to affect sleep.
Next is peanuts or peanut butter, which is a source of niacin. The author claims that niacin can promote serotonin - see above comment regarding oatmeal.
Warm milk is next and the author claims it has tryptophan - see cottage cheese. Also, the calcium in milk can help with melatonin production, so milk will help with sleep! If only it was that easy.
Finally, the author recommends grapes, which supposedly are the only food that contains melatonin. In my opinion, melatonin production is not the problem with most insomniacs.
Eating these foods most likely will not help chronic insomniacs. It could help someone who is just recently suffering from mild difficulty sleeping. This effect most likely would be due to a placebo response.
Relying on things external to our own body, whether it is food, pills, a special blanket, or whatever, probably won't work in the long term and can set up someone to become psychologically dependent on that thing to sleep. In other words, over time, the thing used to help sleep might be paired enough times with actual sleep so that if the thing is not available, the person will not be able to sleep.
Insomnia usually responds better to behavioral therapy, rather than relying on gimmicks like certain foods or other external things.